A board material such as a fiberboard which is manufactured from a slurry-type material is manufactured through a sheet forming process using a sheet forming method. In the manufacture, the sheet forming process using a cylinder type sheet former includes a process of making sheets from the slurry-type material by one or plural cylindrical nets and a process of winding solid components (sheet forming body) formed by making sheets while stacking layers.
This sheet forming method may cause thickness variations of approximately 5 to 30% in a width direction of the manufactured board material as a finished product due to various kinds of factors. As these factors, concentration of materials (quantity of mineral materials or fiber materials) and viscosity thereof, states of a fiber length and a particle diameter, fiber quality, stains in felt, a flow rate of materials, the degree of sinking of materials, time degradation of materials, a circulation direction and velocity by an agitator in a vessel and so on can be cited.
For example, a cylinder type sheet former capable of reducing variations in plate thickness is disclosed in JP-A 2013-112901. The cylinder type sheet former includes discharge means for discharging the slurry from vessels in first and second vessels for storing raw material slurry. The respective discharge means for the first vessel and the second vessel are provided at positioned opposite to each other with the cylindrical net interposed therebetween. According to the structure, the pressure distribution in the vessels can be regulated and variations in plate thickness can be reduced.